There is an increasing need for high luminance colour-tunable light sources, in particular tunable white light sources, but also tunable ultraviolet and infrared light sources, in applications from illumination systems for surgical operating fields, spotlight and data projection systems to a fibre-optical illumination in medical and industrial endoscopy. Concerning white light of high luminance, bright discharge lamps are the state of the art being broadly used today. Recent developments are heading for a combination of solid-state light sources, in particular light emitting diodes (LED) and light converting phosphor elements. Therein, the typically blue or ultraviolet solid-state based light is converted to light having a longer wavelength by a transmission through the phosphor element.
In prior art, a high luminance solid state white light source is obtained for example by arranging a big number of white and colour LEDs in a two-dimensional array, wherein the output colour of such an LED aggregate is tuned by switching on and off the individual colour LEDs.